Lithium secondary batteries have high voltage and high capacity, and thus have been widely used as power supplies of mobile phones, digital cameras, camcorders, notebook computers, electric vehicles and the like. A lithium secondary battery generally distributed contains an electrolyte which is a liquid electrolyte containing an electrolyte salt dissolved in a non-aqueous solvent. As non-aqueous solvents include a number of flammable solvents, there is a need for assuring safety.
For the purpose of assuring safety, an all-solid-state lithium secondary battery has been proposed that contains a so-called solid electrolyte formed from solid materials devoid of the non-aqueous solvent. This all-solid-state lithium secondary battery has a construction provided with a positive electrode, a negative electrode and the solid electrolyte layer positioned between the positive electrode and the negative electrode. The solid electrolyte layer is constituted of a solid electrolyte. Also, the positive electrode and the negative electrode contain a positive electrode active material and a negative electrode active material, respectively, and typically, further contain a solid electrolyte for improving electric conductivity.
A method is known in which the solid electrolyte layer, the positive electrode and the negative electrode are formed to be integrated by pressing starting materials. However, according to this method, the adhesion between the source materials is low, so that it has been difficult to obtain a sufficient electric conductivity.
Thus, a method is proposed in which the positive electrode active material is coated with the solid electrolyte by using a pulse laser deposition technique (Electrochemical and Solid-State Letters, 13(6)A73-A75(2010): Non-Patent document 1, Journal of Power Sources 196(2011)6735-6741: Non-Patent document 2). According to this method, it is assumed that the adhesion between the positive electrode active material and the solid electrolyte becomes high and, for this reason, the electric conductivity can be enhanced.